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參數(shù)資料
| 型號(hào)： | SY87739LHI |
| 廠商： | Micrel Inc |
| 文件頁(yè)數(shù)： | 15/17頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC SYNTHESIZER FRACT 3.3V 32TQFP |
| 標(biāo)準(zhǔn)包裝： | 250 |
| 系列： | AnyClock® |
| 類型： | 分?jǐn)?shù)合成器 |
| PLL： | 是 |
| 主要目的： | 以太網(wǎng)，光纖通道，SONET/SDH/ATM |
| 輸入： | PECL |
| 輸出： | PECL |
| 電路數(shù)： | 1 |
| 比率 - 輸入:輸出： | 1:1 |
| 差分 - 輸入:輸出： | 是/是 |
| 頻率 - 最大： | 729MHz |
| 電源電壓： | 3.15 V ~ 3.45 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 32-TQFP 裸露焊盤 |
| 供應(yīng)商設(shè)備封裝： | 32-EPAD-TQFP |
| 包裝： | 托盤 |
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Micrel, Inc.
SY87739L
June 2011
7
M9999-061511
hbwhelp@micrel.com
Functional Description
General
The SY87739L AnyClock Fractional-N Synthesizer is
used in serial data streaming applications, where the
incoming data rate on a channel may vary, or where the
incoming data rate on a channel is unknown ahead of
time.
In these situations, a valid output stream must still be
generated even in the absence of any edges on the
corresponding input stream. Up until now, designers had
to resort to sub-optimal solutions such as providing
multiple reference oscillators. Beyond the potential noise
and EMI issues, the designer has no way to future proof
his circuit, as it would prove near impossible to pre-
provision all the reference frequencies that might be
needed after deployment, yet are unknown at this time.
The SY87739L solves this problem by generating exact
frequencies for common data streaming protocols, all
from one 27MHz reference. If any of these protocols
include overhead due to use of common digital
wrappers, The SY87739L still generates the exact
frequency required, including the overhead.
Besides
generating
reference
rates
for
common
protocols
directly,
the
SY87739L
also
generates
reference frequencies for Micrel’s SY87721L CDR/CMU,
such that it will reliably recover data at any rate between
28Mbps and 2,700Mbps without any gaps.
A simple 3-wire MicroWire bit-serial interface loads a
configuration that describes the desired output reference
frequency. All common microcontrollers support this
MicroWire interface. Those microcontrollers that don’t
support this interface in hardware can easily emulate the
interface in firmware.
The large set of possible frequencies that the SY87739L
generates, are divided into three classes. First, the sets
of frequencies that match a particular data streaming
protocol are in the “protocol” category. Second, the set
of frequencies that are guaranteed to be near enough to
any arbitrary data rate such that the SY87721L will lock
are in the “picket fence” category. Third, the set of
frequencies that do not fit into either of the first two
categories is in the third category.
The SY87739L generates these important reference
frequencies through two tandem PLL circuits. The first
PLL uses a modified fractional-N approach to generate a
rational
ratio
frequency.
This
PLL
is
capable
of
generating all protocol data rates, except for those that
include FEC or digital wrapper overhead. A second,
more traditional P/Q synthesizer optionally adjusts the
output frequency of the first, fractional-N synthesizer, to
accommodate these FEC or digital wrapper data rates.
The bit serial interface conveys 32 bits of configuration
data from a microcontroller to SY87739L. This simple
interface consists of an active high chip select, a serial
clock (2MHz or less) and a serial data input. Each clock
cycle
one
bit
of
configuration
data
transfers
to
SY87739L.
Circuit Description
The heart of SY87739L is its fractional-N synthesizer, as
shown in Figure 1.
Figure 1. Fractional-N Synthesizer Architecture
The two dividers in the feedback path always differ by
one count. That is, if one divider is set to divide by P = 5,
then the other divider divides by P–1 = 4. The mux
chooses between the two based on the control circuit.
The idea behind the fractional-N approach is that every
input reference edge is used. Only those output edges
that are nearest to an input edge get fed back to the
phase-frequency comparator. In addition, the nearest
output edges are chosen in such a way that the net
offset, over a number of edges, zeroes out. It is the
control circuit’s job to drive the mux such that only the
“correct” edges get fed back.
In the above fractional-N circuit, if the output frequency
should be, for example, 5 times the input frequency, then
P is set to 5, and the control circuit sets the mux to only
feed back the output of the P divider.
If the output frequency should be, for example, 41/2
times the input frequency, then the control circuit
alternates evenly between the P and the P–1 divider
output. For every two input edges (one to compare
against P, and another to compare against P–1), you will
get 5 + 4 output edges, yielding an output frequency 9/2
the input frequency.
or (408) 955-1690
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SY87739LHITR | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:PROTOCOL TRANSPARENT 3.3V 10MHz to 729MHz FRACTIONAL-N SYNTHESIZER |
| SY87739LHY | 功能描述:時(shí)鐘合成器/抖動(dòng)清除器 3.3V Fractional N Synthesizer (10MHz to 729MHz) (Lead Free/I Temp/32 pin TQFP) RoHS:否 制造商:Skyworks Solutions, Inc. 輸出端數(shù)量: 輸出電平: 最大輸出頻率: 輸入電平: 最大輸入頻率:6.1 GHz 電源電壓-最大:3.3 V 電源電壓-最小:2.7 V 封裝 / 箱體:TSSOP-28 封裝:Reel |
| SY87739LHY TR | 功能描述:時(shí)鐘合成器/抖動(dòng)清除器 3.3V Fractional N Synthesizer (10MHz to 729MHz) (Lead Free/I Temp/32 pin TQFP) RoHS:否 制造商:Skyworks Solutions, Inc. 輸出端數(shù)量: 輸出電平: 最大輸出頻率: 輸入電平: 最大輸入頻率:6.1 GHz 電源電壓-最大:3.3 V 電源電壓-最小:2.7 V 封裝 / 箱體:TSSOP-28 封裝:Reel |
| SY87739LHYTR | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:PROTOCOL TRANSPARENT 3.3V 10MHz to 729MHz FRACTIONAL-N SYNTHESIZER |
| SY87813L | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:3.3V, 28Mbps to 1.3Gbps AnyRate Clock and Data Recovery |
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